External reducing valves

NW Mailing List nw-mailing-list at nwhs.org
Mon Feb 11 11:46:39 EST 2019

Ed ,Jimmy, and Dave 


  Thanks much for your answers . I am confused mostly in my wording to you . I do understand the function.  Now did the external reducing

valve(improved intercepting valve) and booster valve modifications go hand in hand ?? or did the external reducing valve precede the booster valves on some locomotives?? Still amazing and a tribute to the N&W MP Dept. and shop force to have done all this  at such a late date in steam.  I been working on a mallet

locomotive for the last year (you can guess) and we are getting close on reinstalling the intercepting valve and exhaust valve(Alco 1910 version) and that’s what 

got me thinking on this just trying to get my head around it.  I always say I know a little about everything and a whole lot about nothing. Thanks again Ed your 

expertise is always appreciated. If you and Bud are still working on the compound book hope you cover this in detail.



Larry Evans

Kenova WV 


From: NW-Mailing-List [mailto:nw-mailing-list-bounces at nwhs.org] On Behalf Of NW Mailing List
Sent: Monday, February 11, 2019 10:32 AM
To: nw-mailing-list at nwhs.org
Subject: RE: External reducing valves


Ed, Are you and Bud still considering a new text on the Y Class locos?    Thanks,  John Garner


From: NW Mailing List [mailto:nw-mailing-list at nwhs.org] 
Sent: Sunday, February 10, 2019 10:30 PM
To: NW Mailing List <nw-mailing-list at nwhs.org <mailto:nw-mailing-list at nwhs.org> >
Subject: Re: External reducing valves


Larry - 


You have a few things confused here.  Alco developed an intercepting valve about 1910 for Mallet locomotives which automatically started the locomotive out in simple operation – in other words, live steam from the throttle into all four cylinders.  In order for this steam at high pressure not to cause the front engine to slip because of the larger cylinders, a reducing valve was incorporated to limit the pressure of this steam going to the bigger low-pressure cylinders so the front engine wouldn’t be slippery.  All N&W’s Alco Mallets had this feature and it was adopted as the standard for all the Mallets built by Roanoke.  Starting out in simple was automatic.  Also provided was a so-called “emergency” valve which could be operated by the engineer to keep the intercepting valve from functioning – in other words, to keep the engine operating in simple cycle until a difficult situation could be dealt with.  This is not the same as the emergency valve incorporated into the air brake valve.


When the improved intercepting valve was developed (in the early 1950s, I believe – someone correct me if I’m wrong) an external reducing valve was used which appeared as a cylindrical gadget above the right high-pressure valve chest.  When this was done, control of the simpling function was no longer automatic but was given to the engineer in the form of a lever in the cab that he could use as conditions required.  But simpling still required the use of the reducing valve.


The so-called “booster” valve which added a measured amount of throttle steam to the receiver to increase the power of the low-pressure engine was a separate valve under the control of the engineer so as to increase the power of the low-pressure engine after the engine had been changed from simple at starting and low speed to give the engine a bit more power under difficult circumstances.  All the 2100-series Y’s got this feature.  None of the earlier ones did, nor did the Z’s.  As these features were developed, all the 2100s were retrofitted so that N&W had 100 locomotives of equal capability.  If you had the 2101 out on the side of the mountain with tonnage, you would not be any better off with the 2200.


These features made N&W’s 2100-series Mallets far and away more powerful than anyone else’s Mallets.  The Y-2 of 1918 pointed the way, and the USRA Y-3s and descendents were far and away faster than all the others.  When you consider that the horsepower curve of a Virginian AE 2-10-10-2 peaked out at 8 MPH and that of a Y-6 peaked out about 30 (at 5500 DBHP) you can see why N&W took the trouble to keep on developing the Y engines.  I know, the AE had ten thousand pounds more starting tractive effort than the 2100, but that figure was good for bragging rights and that was about all.


Hope this helps and is not tMI.


Ed King




From: NW Mailing List 

Sent: Sunday, February 10, 2019 8:29 PM

To: nw-mailing-list at nwhs.org <mailto:nw-mailing-list at nwhs.org>  

Subject: External reducing valves


N&W in early fifty’s started using the external reducing valves on the Y classes. Which enable them also to manually to control the intercepting valve and

put superheated steam into the LP receiver  While running it compound.  Anyone have an idea exactly  what locomotives actual got this modification? 

All Y6bs ??  I know some Y5s.   I have heard all Y6bs but at this late date seems to me to be improbable?  Thanks for any help.      






Larry Evans

Kenova WV


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